I started photography as a hobby and now it is changing into something new that i have no experience in yet. I was asked to take some pictures for a Birthday party, a friend asked me to take Nude photography for her, and a couple friend that asked me to take pictures for their nice cars, etc...

I never charge anything in the past. so i have no clue how to handle these offer.
What are the price range? do we charge by hours?
Can someone explain it to me?
i want to be fair for me and my clients.

A similar question was asked about pricing, but for weddings. The principle behind how to approach pricing is the same though, and I have written an answer here.

As an aside, do think about the lighting if you plan to do artistic nudes - soft light is what you should be thinking of, and if you need artificial light, 1-strobe/studio flash with softbox/umbrella should be all you need, if you're not considering using natural window light.

I am a student, I charge or got paid $50 / hour for short events (less than 3 hours), for long hours event, it is more flexible or cheaper / hour.

I usually don't have to travel because the client is the university itself.

Sometime, I do shoot outside sports event, and sell prints to parents. The income from this depending on how big is the event and how willing the parents to buy pictures.

You'll need to analyze the condition and situation, for example, how's the competitor charging? how good is your photos comparing to competitors in the area. If you are the only one (or competitor is low) and your skills are better comparing to other photographers, then you might charge a little bit more.

What I know is experienced professional wedding photographers usually charge around US$2500 / 12 hours = $208 an hour but this is not including post processing hours, travel, assistant(s) pay if you use any plus the printing costs. Probably the net income will be around $100 / hour

I also don't recommend charging too cheap, because soon you charge that price, it is become standard, and it is very hard to raise the price because your clients will feel that you overcharge them. Go for moderate charge and if your client feels it is too expensive, you can decrease your price down a bit.